Function highlight 

pub fn highlight(code: &str, language: &str) -> Vec<Token>

Highlight code as language and return a de-duplicated, left-to-right sorted list of tokens with UTF-16 offsets.

Errors

Returns an empty vector (not an error) when:

• the language is not supported — callers render plain text
• the code is empty — no tokens to produce

Grammar-compilation or parse failures are recoverable: we return an empty vector and the caller paints plain text. We never panic.